# Exec error op\_readKN

**URL:** <https://community.freefem.org/t/exec-error-op-readkn/321>\
**Category:** General Discussion\
**Created:** [April 7, 2020, 10:13pm UTC](https://community.freefem.org/t/exec-error-op-readkn/321 "2020-04-07T22:13:32Z")\
**Posts on this page:** 2\
**Page:** 1

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**Author:** ![littleprg](https://avatars.discourse-cdn.com/v4/letter/l/35a633/32.png) [@littleprg](https://community.freefem.org/u/littleprg)\
**Post date:** [April 7, 2020, 10:13pm UTC](https://community.freefem.org/t/exec-error-op-readkn/321/1 "2020-04-07T22:13:32Z")

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Hello everybody. I’m new at using freefem and I started using a code which may have to work of a simulation of a mechanical problem.  
Running the code I repeatedly got this exec error:  
Fatal error in op\_readKN(array)  
Can someone help me in undestanding the reason of this? I didn’t really found what this kind of warning stands for.  
Thank you in advance!

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**Author:** ![prj](https://avatars.discourse-cdn.com/v4/letter/p/ecae2f/32.png) [@prj](https://community.freefem.org/u/prj)\
**Post date:** [April 8, 2020, 6:04am UTC](https://community.freefem.org/t/exec-error-op-readkn/321/2 "2020-04-08T06:04:08Z")

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Please provide a minimal working example ([MWE](https://en.wikipedia.org/wiki/Minimal_working_example)) if you want us to help you out. This is probably due to a mismatch in array sizes, between the one defined in your script and the one you are reading from file.